A printed wiring board formed by laminating prepreg containing a core material on a core substrate containing a core material such as glass fiber is widely used as a package substrate for mounting an electronic component. Patent publication (1) discloses setting the elastic modulus of interlayer insulation layers made of prepreg to be lower than that of the core substrate in a composite substrate formed by laminating prepreg on a core substrate. Patent publication (2) discloses setting the thermal expansion coefficient of buildup layers to be 70 ppm/° C. or lower in a multilayer printed wiring board formed by laminating buildup layers on a core substrate. Patent publication (3) discloses setting the thermal expansion coefficient of interlayer insulation layers to be 35 ppm or lower in a multilayer circuit board formed by laminating single-sided substrates. Patent publication (4) discloses adjusting thicknesses of a core substrate and first and second interlayer insulation layers. Patent publication (5) discloses laminating on a printed wiring board a thermal expansion buffer sheet with a thermal expansion coefficient of 6˜13 ppm.